Ionic and Covalent bonding: MCQ 4
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Questions and Answers

What is the purpose of adding NaF (sodium fluoride) to water?

  • To preserve foods such as bacon
  • To prevent tooth decay (correct)
  • To replace salt lost through sweating
  • To identify anions in a solution
  • Which of the following tests is used to identify the presence of carbonate anions?

  • Adding dilute HCl to the solution (correct)
  • Mixing the solution with cold concentrated H₂SO₄
  • Adding BaCl₂ to the solution
  • Adding ammonium molybdate reagent and concentrated nitric acid
  • What is the result of adding BaCl₂ to a solution containing sulfate anions?

  • A white precipitate is formed that is soluble in dilute HCl solution
  • A white precipitate is formed that is insoluble in dilute HCl solution (correct)
  • A brown ring is formed
  • A yellow precipitate is formed
  • What is the purpose of adding a few drops of dilute ammonia solution to a solution containing chloride anions and AgNO₃?

    <p>To dissolve the white AgCl precipitate</p> Signup and view all the answers

    What is the result of mixing a nitrate solution with cold concentrated H₂SO₄?

    <p>A brown ring is formed</p> Signup and view all the answers

    What is the result of adding dilute Hydrochloric acid to a carbonate or a Hydrocarbonate compound?

    <p>Bubbles of Carbon dioxide are produced</p> Signup and view all the answers

    What is the purpose of adding ammonium molybdate in the test for Phosphate (PO₄³⁻) anion?

    <p>To produce a yellow precipitate</p> Signup and view all the answers

    What is the characteristic of covalent compounds that allows them to conduct electricity when molten or in solution?

    <p>They break up to form ions</p> Signup and view all the answers

    What is the term for the ability of an atom in a covalent bond to attract the shared pair of electrons?

    <p>Electronegativity</p> Signup and view all the answers

    What is the type of bond that is formed when the difference in electronegativity values between atoms is greater than 1.7?

    <p>Ionic</p> Signup and view all the answers

    Why is it essential to use the minimum amount of hot water when dissolving benzoic acid crystals?

    <p>To ensure the maximum yield of benzoic acid crystals at the end of the experiment</p> Signup and view all the answers

    What happens when the benzoic acid solution is cooled to room temperature and then placed in iced water?

    <p>The benzoic acid starts to recrystallize</p> Signup and view all the answers

    What is the purpose of filtering the solution by vacuum filtration?

    <p>To separate the benzoic acid crystals from the insoluble impurities</p> Signup and view all the answers

    What is the effect of impurities on the melting point of benzoic acid?

    <p>Decrease the melting point of benzoic acid</p> Signup and view all the answers

    What is the expected melting point range of pure benzoic acid?

    <p>121° - 122°</p> Signup and view all the answers

    Study Notes

    Importance of Salt

    • Isotonic salt tablets are taken by athletes to replace salt lost through sweating
    • Brine (salt solution) is used to preserve foods such as bacon
    • NaF (sodium fluoride) is added to water to prevent tooth decay

    Identification of Anions

    Tests for Various Anions

    • Carbonate and Hydrogencarbonate: Add dilute HCl to the solution, and a gas is produced that turns limewater milky
    • Carbonate: Add BaCl₂ to the solution, and a white precipitate forms
    • Hydrogencarbonate: Add BaCl₂ to the solution, and a white precipitate forms on heating
    • Sulfate: Add BaCl₂ to the solution, and a white precipitate forms that is insoluble in dilute HCl solution
    • Sulfite: Add BaCl₂ to the solution, and a white precipitate forms that is soluble in dilute HCl solution
    • Chloride: Add AgNO₃ to the solution, and a white precipitate forms that is soluble in dilute NH₃ solution
    • Nitrate: Mix the solution with cold concentrated H₂SO₄, and a brown ring forms
    • Phosphate: Add ammonium molybdate reagent and concentrated nitric acid, heat gently, and a yellow precipitate forms that is soluble in ammonia solution

    Properties of Covalent Compounds

    • Most are liquids or gases at room temperature, or solids with low melting and boiling points
    • They do not conduct electricity when molten or in solution because they do not break up to form ions
    • Most covalent substances do not dissolve readily in water

    Electronegativity

    • Electronegativity is the relative attraction of an atom for the shared pair of electrons in a covalent bond
    • Electronegativity values can be used to determine which atom will have the greater attraction on the shared pair of electrons
    • Examples: Hydrochloric acid (H-Cl) has a polar covalent bond, with chlorine having a greater electronegativity value

    Predicting Bonds

    • Electronegativity values can be used to predict the type of bond that will be formed between atoms
    • The greater the difference in electronegativity values between atoms in a bond, the greater the degree of polarity
    • Examples:
      • Non-polar covalent bond: CS₂, Cl₂
      • Polar covalent bond: HBr
      • Ionic bond: NaCl

    Recrystallization of Benzoic Acid

    • Benzoic acid is a crystalline solid that is very soluble in hot water but only slightly soluble in cold water
    • The experiment involves dissolving the original crystals, removing impurities, and recrystallizing pure benzoic acid crystals
    • The final mass of the crystals is measured, and the melting point of the recrystallized benzoic acid is found

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    Test your knowledge of inorganic compounds with these questions about sodium fluoride, carbonate anions, and sulfate anions.

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